In a railroad vehicle, an air spring is arranged between a vehicle main body and a carriage in order to reduce impacts and vibrations applied to a vehicle body during traveling of the vehicle. The air spring mainly includes: an upper surface plate connected to the vehicle main body; a lower surface plate arranged below the upper surface plate; a diaphragm made of rubber and arranged so as to connect the upper surface plate and the lower surface plate; and the like. The diaphragm is elastically deformed, so that impacts and vibrations applied in the upward and downward directions during traveling of the vehicle can be reduced.
The air spring has an air supply/discharge valve (leveling valve) for supplying/discharging pressurized air into/from the air spring. The air supply/discharge valve has a dead band, and is controlled to be closed in a normal case (in the case where impacts and vibrations are not relatively large). In this case, the air spring acts to reduce the impacts and vibrations applied to the vehicle by elastic deformation of the diaphragm as described above. On the other hand, for example, when the payload applied to the vehicle is increased to thereby lower the vehicle height, or when the centrifugal force generated during turning traveling of the vehicle acts to lower the vehicle height at a distal portion of the vehicle relative to a center of the turning traveling, the air supply/discharge valve (leveling valve) is opened to supply the pressurized air within an air reservoir into the air spring. Thereby, the height of the upper surface plate can be raised relative to the lower surface plate. In this way, the vehicle height can be controlled to be set at a prescribed height by controlling the amount of pressurized air to be supplied into the air spring.
The railroad vehicle is generally provided with a fail safe function in preparation for the case where the air supply/discharge function is not normally performed.
For example, in the case where the fail safe function is implemented using a sensor detecting a change of the vehicle height (electrical processing) and an air-discharge solenoid valve for discharging air in response to a detection signal from the sensor, there occur problems that the structure and the system of the air spring become complicated.
In consideration of the above-described problems, Japanese Patent Laying-Open No. 11-78877 discloses, as a mechanism for preventing excessive supply of pressurized air into the air spring, an air spring apparatus for supporting vehicle body configured in such a manner that air inside the air spring can be discharged by causing an arm to directly contact a diaphragm while air is being excessively supplied.